Tetrakis nf2 adduct of divinylcarbinol and acrylate and polymer thereof



United States Patent This invention relates particularly to the synthesis and polymerization of 3-(l,2,4,5-tetrakis-(NF )-pentyl) acryla te which forms a polymer of suitable characteristics for use as a binder in a high-energy solid rocket propellant.

An objective is to develop a polyacrylate which contain a high NF content, and a difiiculty in achieving this objective has been the preparation of suitable monomeric components.

In accordance with the present invention, it has now been found that the unsaturated alcohol divinylcarbinol, or 1,4-pentadiene-3-ol, having the formula can be reacted under suitable conditions to prepare a high NF content alcohol that is satisfactorily esterified to form a polymerizable acrylate useful for polymerization to form a desired clear, tough resin of high NF content.

The reaction of divinylicarbinol with N 1 can be carried out satisfactorily under superatmospheric pressure in the range of about 100 to 500 p.s.i. at programmed temperatures in the range of 50 to 150 C., and at a maximum in the range of 120 to 150 C., using a glass reactor or a stainless steel reactor. In using a glass reactor, the reactor is preconditioned by treatment with HF and the reaction is preferably run using an NaF buffer in the amount of 5 to by weight of the carbinol.

In some of the first attempts to form the tetrakis NF adduct of divinylcarbinol, there was an observation that at lower reaction temperatures in the range of 50 to 100 C., the product obtained was mainly the bis NF adduct. In using more drastic conditions involving reaction temperatures up as high as about 200 C., there was some loss of fluorine.

The following example demonstrates a preferred method of obtaining the tetrakis NF divinylcarbinol adduct particularly suitable for esterification with acid or acrylic chloride to obtain a polymerizable acrylate represented by the following formula:

Example Divinylcarbinol (10% solution in CHCl is reacted with excess N 1 for saturating the double bonds under a pressure in the range of 200 to 500 p.s.i. at a programmed reaction temperature at 50 C. for 1 hr., 100 C. for 1 hr., and with a final temperature ranging principally from 120 C. to about 140 C. for a final reaction period of 2 to 3 hours. The crude product obtained was found to contain from 50 to 75 wt. percent of the tetrakis NF adduct of the divinylcarbinol. This crude product is reacted with excess acrylyl chloride using zinc chloride as the esterification catalyst at a temperature in the range of 30 to 80 C. under a reduced pressure of about 100 mm. Hg absolute for a period in the range of 30 minutes to 2 'hours to form the 3-(l,2,4,5-tetrakis-(NF )-pentyl) acrylate having a structural formula as indicated.

The acrylate can be purified by short-path vacuum distillation. Column chromatography on silica gel, with the 3,441,550 Patented Apr. 29, 1969 use of CHCI or similar solvent for elution, or gas chromatography can also be used for isolation of the substantially pure product having a composition corresponding to the theoretical composition for the structural formula given, ifi. C8H10O2N4F3.

The tetrakis NF pentyl acrylate is polymerized with an organic peroxide catalyst, such as benzoyl peroxide, (0.l to 10 wt. percent of catalyst) at a moderate temperature of about C., or in the range of 2S to C., to obtain a rubbery solid in several hours. The rubbery solid, on further heating for 20 to 25 hours, yields a clear, tough resin of 60% NF content, and this resin is useful as a binder in a solid rocket propellant composite, as shown by its physical characteristics and high-energy'productrThe composition and structure assigned to the linear acrylate polymer obtained is:

lTlFg NF: NF; NF: CHr-CH-CH-CH-CH;

wherein the subscription n, in the usual manner, indicates the number of recurring monomeric units in the linear polymer chain. This acrylate polymer is indicated to have molecular weights in the range of 2,000 to 40,000 and higher. Polymers thus obtained have substantial solubility in acetone.

In the preparation of the tetrakis NF adduct of divinylcarbinol, modifications may be made. For example, other halogenated aliphatic hydrocarbons may be used as the solvent or diluent for the divinylcarbinol, e.g.

In forming the polymers, a low molecular weight prepolymer of viscous liquid consistency may be formed for compositing with powdered metal fuels of high energy and solid and liquid oxidizers of high energy to further polymerization during casting of the propellant grain. If desired, the polymer composite can be put into a solution with acetone as the solvent, or a similar liquid solvent, for compositing.

High specific impulse composites are obtained with the polyacrylate binder made in accordance with the present invention using this polymer in a proportion of about 5 to 20 wt. percent with about 2 to 10 wt. percent of a powdered metal fuel, such as boron, beryllium, aluminum or lithium, and using suitable proportions of solid oxygencontaining oxidizers, such as nitrates, perchlorates, or polynitro compounds, and liquid NF compounds, such as tetrakis NF; butane, that serve as oxidizers and plasticizers.

The invention described is claimed as follows:

1. Tetrakis NF adduct of divinylcarbinol.

2. Acrylate of tetrakis N1 adduct of divinylcarbinol represented by the formula:

3. Polymer of 3-(l,2,4,5-tetrakis-(NF )-pentyl) acrylate.

4. Method of synthesizing tetrakis NF adduct of divinylcarbinol, which comprises reacting divinylcarbinol dissolved in a halogenated aliphatic hydrocarbon solvent with excess N F under pressure at a programmed temperature to a maximum of to C. to obtain a product having 50 to 75 wt. percent of tetrakis NF adduct of the divinylcarbinol.

5. Method of forming 3-(1,2,4,5-tetrakis-(NF )-pentyl) acrylate, which comprises reacting tetrakis NF adduct of divinylcarbinol with acrylyl chloride in the presence of a catalyst at 30 to 80 C. under reduced pressure for about 30 minutes to 2 hours and recovering as resulting product a crude acrylate having the composition C H O N F and separating said resulting product.

6. Process for preparing a high-energy polyacrylate, which comprises treating 3-(1,2,4,5-tetrakis-(NF )-pentyl) acrylate in with an organic peroxide catalyst until the acrylate monomer is polymerized to a solid.

7. Process for preparing a high-energy polyacrylate suitable as a solid rocket propellant, which comprises: (a) synthesizing tetrakis NF adduct of divinylcarbinol by reacting divinylcarbinol with N F (b) reacting said tetrakis NF; adduct of divinylcarbinol with acrylyl chloride as an acrylic esterification reactant to form an acrylate of said tetrakis NF adduct of divinylcarbinol; (c) polymerizing said acrylate.

8. Process of claim 7, wherein the acrylate has the formula:

and the acrylate is polymerized to a polymer characterized by the recurring unit:

wherein the subscript 11 indicates the number of recurring units to give the polymer a molecular weight in the range of 2,000 to about 40,000.

9. Process of claim 7, wherein the acrylate polymer is heated to obtain a clear, tough resin to rubbery solid.

References Cited Hoffman et al.: Chemical Reviews, vol. 62, pp. 12 to 18 (1962).

LELAND A. SEBASTIAN, Primary Examiner.

US. Cl. X.R. 

1. TETRAKIS (F2 ADDUCT OF DIVINYLCARBINOL.
 2. ACRYLATE OF TETRAKIS NF2 ADDUCT OF DIVINYLCARBINOL REPRESENTED BY THE FORMULA:
 3. POLYMER OF 3-(1,2,4,5-TETRAKIS-(NF2)-PENTYL) ACRYLATE. 